Compliance with present and future emission standards requires an exhaust aftertreatment in internal combustion engines. Thus, for example, conventionally, common rail diesel engines require a system for regenerating a particle filter which is provided for exhaust gas treatment, whereby structural engine measures must be taken in order to increase the filter temperature for purposes of regeneration, and optionally to set the recirculation rate of an exhaust gas recirculation (EGR) system with the aid of an EGR valve and/or to set the feed rate of a fresh air mass with the aid of a throttle valve. In particular, reducing the EGR rate and supplying a larger fresh air mass by opening the throttle valve are used to increase the filter temperature.
In addition, for a fuel injection system discussed here, conventionally, post-injections are provided which are not instantaneously effective and are relatively late in terms of time, which react at the particle filter. The fuel quantity injected during the post-injection must be metered very precisely, the injection usually being divided into multiple partial injections following one another in rapid succession.
Examples of possible negative effects of an incorrectly metered post-injection include recirculation of uncombusted fuel, via the EGR, into an intake manifold of the internal combustion engine, an excessive temperature during the combustion in the particle filter due to a post-injection quantity that is too high, resulting in damage to filter components, and an excessively low temperature of the particle filter due to a post-injection quantity that is too low, so that regeneration is not possible.
Conventionally, the calibration or correction of late post-injections discussed here takes place indirectly with the aid of a temperature controller, the filter temperature being detected at or near the particle filter, and a correction being made to a temperature setpoint value stored in a control unit of the internal combustion engine. The entire setpoint quantity of the post-injection is used as the manipulated variable, individual injections not being taken into account or corrected.
One disadvantage of this procedure is that the concurrent correction of all partial injections may result in impermissible deviations of individual partial injections, and a mentioned temperature controller must be configured for each individual engine.
In the passenger vehicle sector, it is also conventional to correct pre-injections based on engine speed, for example with the aid of the conventional zero fuel calibration (ZFC) method. This calibration method requires a particular operating mode of the internal combustion engine or of the motor vehicle, for example coasting mode. However, it has been shown that a transfer of the ZFC learned values from pre-injections to late post-injections is possible only to a very limited extent, since the exhaust gas back-pressures differ greatly for various crank angle positions of the start of injection. An appropriately carried out back-pressure compensation is possible, but is associated with a high level of technical effort, and thus increased costs.
In the truck and commercial vehicle sector, the mentioned corrections of pre-injections are likewise carried out based on engine speed, the calibration taking place at idle speed of the internal combustion engine.
In addition, a method is described in German Patent Application No. DE 102 32 356 A1 for controlling injectors of a fuel metering system discussed here, in which the start of injection and the end of injection, and on this basis the injection time, which is a measure for the injected fuel quantity, are determined with the aid of a pressure sensor situated at a high-pressure fuel accumulator (rail). In particular, it is provided in the cited document that the values thus ascertained are compared to stored values, and in the event of a deviation of the start of injection, the injection duration is corrected in such a way that the deviation is eliminated.